Irfan Raja's parents alerted police after being left a letter from him

The chain of events which led to five young Muslim men being convicted for downloading extremist literature was triggered by a letter a schoolboy wrote to his parents.

"Please do not blame each other for why you couldn't stop me," Irfan Raja wrote in his neat hand to his mother and father.

"Just in case you think I am going to [do] something in this country, you can rest easy that I am not. The conventional method of warfare is safer."

Irfan childishly draws a dotted line across the piece of paper and advises his parents in a "PPS" that if they wish to keep the letter, they should destroy the letter above the line as "these people (of the UK) use everything against you".

He ends with "Now smile!".

Irfan then stuffed the note under his mattress and ran away from home, saying he was planning to fight abroad in the name of Islam. He also took his passport and left a martyrdom song on the family computer.

He had met a group of Bradford University students on online chatrooms used by extremist recruiters.

One of them - Awaab Iqbal - paid for Irfan's bus ticket and the teenager went and stayed with Mr Iqbal and his friend Aitzaz Zafar.

Irfan lost his nerve and returned home to Ilford within days, after his parents begged him in a telephone call to come back, but it was too late. His parents had shown his letter to the police.

He, Mr Iqbal and Mr Zafar - along with Usman Malik and Akbar Butt - were arrested. The material gathered from them led to the convictions for downloading and sharing extremist terrorism-related material which have now been quashed at the Appeal Court.

The material included publications popular among extreme Islamist organisations, encouraging Muslims to fight.

One of the five had also used a computer to superimpose his own face on a montage of the 9/11 hijackers.

The trial heard police found material on their computers downloaded from the internet, and chatroom conversations said to be intended to encourage terrorism or martyrdom.

Among the items found was a film showing atrocities against Muslims around the world, aimed at encouraging martyrdom.

Prosecutors said the men also had a US military guide to terrorism and a suicide bombing manual.

But their lawyers said the law was designed to catch people holding plans for bombs rather than propaganda.

None of the men possessed information suggesting they were plotting a bomb attack, although there had been talk of heading to Pakistan for paramilitary training.

The five men were jailed in 2007 for between two and three years each by the Old Bailey.